For a normal distribution, use a standard normal distribution table or a technology to complete parts a through c. Click here to view page 1 of the standard normal table. Click here to view page 2 of the standard normal table. a. Find the probability that an observation is at least 1 standard deviation above the mean. The probability is 0.159 . (Round to three decimal places as needed.) b. Find the probability that an observation is at least 1 standard deviation below the mean. The probability is (Round to three decimal places as needed.)